Costs - Extra year of going to school (which at many places can amount to an extra 60-70k)

Aid - Dunno

Apply - You can apply prior to school as a JD/MBA or, at some places, you can try and "backdoor" into it and apply during your first year.

Helps - It doesn't really help. The jobs just don't overlap enough for employers to value a JD/MBA over a JD. Even if employers did care, it would have to be a worthwhile MBA program and the number of universities that have both good law schools and good business schools is very minimal.